In testing a sustained release drug, a capsule, pellet, tablet or other form of the pharmaceutical product is exposed for a predetermined and reproducible time period to a selected solvent having a controlled pH. At the end of the exposure period, the solvent is separated from undissolved residue, and a new solvent with an increased pH is added to the residue. After several such solvent changes, the solutions are assayed, and the percentages of dissolution are determined. A typical device used in carrying out the above procedure is shown in U.S. Pat. No. 3,742,190.
Current methods require that an operator be present to change and collect the used solvents for assay. Although more than one sample may be run simultaneously, the manual procedure is still time consuming.